[рони]

mrmammoth,

<script>
    var arr = [{"param1":"volume1","param2":"volume2"}]

   function doAdd(params) {

            !arr[0]['param3'] && (arr[0]['param3'] = [])

                    arr[0]['param3'].push(params);

            return JSON.stringify(arr);
}
document.write(doAdd({"param1":"value1","param2":"value2"})+"<br>")
document.write(doAdd({"param1":"value1","param2":"value2"})+"<br>")
document.write(doAdd({"param1":"value1","param2":"value2"})+"<br>")
</script>